The broadband wireless access (BWA) has attracted increasing attention as it accelerates the access rate of communication system.
In terms of the fundamentals of radio communications, the higher the radio wave transmission frequency is, the faster the attenuation over a longer communication distance will be. Conventional wireless relay systems rely mostly on centralized scheduling, and the Multihop Relay Base Station (MR_BS) allocates one Code Division Multiple Addressing (CDMA) Ranging Code subset to each Relay Station (RS) in the relay link to reduce overhead on wireless multi-hop networks and delay in each ranging process. A part of the RS CDMA Ranging Code may be used to inform the MR-BS that Mobile Station (MS) need to request bandwidth for forwarding a bandwidth request header to the MR-BS, while the other part may be used to inform MR-BS that RS need to request bandwidth for forwarding a bandwidth request header to MR-BS. RS forwards the bandwidth request of MS to MR_BS in the relay uplink. After receiving CDMA ranging code which is used for the bandwidth request, MR_BS allocates uplink bandwidth to the corresponding access link and relay link so that the MS can send a bandwidth request header to MR_BS.
In the multi-hop network with RSs, the MS sends the CDMA ranging code to its severing RS, to request bandwidth allocation used for sending the bandwidth request header. After receiving the CDMA ranging code from MS, RS sends on its own uplink the CDMA ranging code of RS corresponding to the CDMA ranging code from MS. If several RSs are available, each RS sends the CDMA ranging code, on its own uplink, to request bandwidth allocation till the CDMA ranging code of bandwidth request is sent to MR_BS. After receiving the CDMA ranging code, MR_BS allocates uplink bandwidth to RS and requires the RS to send the MR_Code_REP message to MR_BS. RS sends the MR_Code_REP message to inform MR_BS that an MS within its coverage requests for sending a bandwidth request header to MR_BS. The MR_Code_REP message includes the CDMA ranging code from MS. MR_BS may use the related information contained in MR_Code_REP message to allocate the uplink bandwidth to MS and requires the MS to send a bandwidth request header.
In the conventional system, the Orthogonal Frequency Division Multiplexing (OFDM) physical layer uses the Raphael pseudo noise sequence code ranging code, i.e. CDMA ranging code.
Up to 256 ranging codes are available and it ranges from 0 to 255. Each MR_BS uses one subset of these codes, wherein the subset is defined by S, 0<=S<=255. The codes in the subset are made up of codes between S and ((S+O+N+M+L) mod 256). Wherein, the first N codes are used for initial ranging, the following M codes are used for periodic ranging; the latter L codes are used for bandwidth request, and the following O codes are used for switching ranging.
MS sends the CDMA ranging code to MR_BS. When MR_BS detects the CDMA ranging code, it will allocate uplink bandwidth to MS through broadcast message(s) and the CDMA-allocation-IE in such broadcast message indicates the transmission area and the CDMA ranging code sent by MS. Then, through parameters such as the CDMA ranging code in this message, MS confirms that the bandwidth in this message is allocated to it. Therefore, MS can use the allocated bandwidth to send bandwidth requests or data. MR_BS may receive several CDMA codes at the same time.
FIG. 1 shows the process where the MS requests bandwidth for sending data packets via CDMA ranging codes in a wireless relay system including two RSs, such as RS1 and RS2. MR_BS sends a UL_MAP message to MS, RS1, and RS2 through broadcast. The UL_MAP message mainly defines uplink parameters. MR_BS allocates bandwidth which is defined by IE in UL_MAP to MS and RS for sending uplink data and messages. Each frame has a UL_MAP. The specific signaling flows are as follows:
Step 1: MR_BS broadcasts the UL_MAP message to MS, RS1, and RS2. FIG. 1 shows that MS receives the UL_MAP message sent by MR_BS through broadcast. Actually, MS may receive the UL_MAP message directly from MR_BS, or receive the UL_MAP message forwarded by relay stations. Similarly, the UL_MAP message received by RS1 may be directly sent from MR_BS, or forwarded by RS2.
Step 2: MS sends CDMA ranging code to its severing RS1 for requesting uplink bandwidth, and the CDMA ranging code sent by MS is identified as MS_CDMA ranging code.
Step 3: After receiving the MS_CDMA ranging code, RS1 stores the MS_CDMA ranging code, generates a new CDMA ranging code according to the CDMA ranging code subset which is allocated by MR-BS, and sends the new CDMA ranging code to RS2 to request uplink bandwidth; and the CDMA ranging code sent by RS1 is identified as RS1_CDMA ranging code.
Step 4: After receiving the RS1_CDMA ranging code, RS2 forwards it to MR_BS.
Step 5: After receiving the RS1_CDMA ranging code, MR_BS broadcasts the UL_MAP message which contains the information about allocating uplink bandwidth to RS1. RS1 obtains the uplink bandwidth by parses the information in the UL_MAP message. FIG. 1 shows that RS1 directly receives the UL_MAP message sent by MR_BS through broadcast. Actually, RS1 may also receive the UL_MAP message sent by RS2.
Step 6: RS1 uses the uplink bandwidth allocated by MR_BS to send the MR_Code_REP message carrying with the stored MS_CDMA ranging code information to RS2.
Step 7: After receiving RS1_CDMA ranging code, MR_BS broadcasts the UL_MAP message, which contains the information of allocating the uplink bandwidth to RS2. RS1 obtains the uplink bandwidth by parsing the information in the UL_MAP message.
Step 8: After obtaining the uplink bandwidth, RS2 forwards the MR_Code_REP message to MR_BS.
Step 9: After receiving the MR_Code_REP message, MR_BS reads the content of the message and obtains the MS_CDMA ranging code information. MR_BS allocates corresponding uplink bandwidth to MS. Specifically, MR_BS broadcasts the UL_MAP message, which contains the information about allocating the uplink bandwidth to MS. FIG. 1 shows that MS directly receives the UL_MAP message from MR_BS through broadcast. Actually, MS may also receive the UL_MAP message forwarded by relay stations.
Step 10: MS sends a bandwidth message header to RS1 by using the uplink bandwidth allocated by MR_BS.
Step 11: MR_BS broadcasts the UL_MAP message, which contains the information about allocating the uplink bandwidth to RS1. FIG. 1 shows that RS1 directly receives the UL_MAP message sent by MR_BS through broadcast. Actually, RS1 may also receive the UL_MAP message forwarded by RS2.
Step 12: RS1 uses the allocated uplink bandwidth to forward the received bandwidth message header to RS2.
Step 13: MR_BS broadcasts the UL_MAP message, which contains the information about allocating the uplink bandwidth to RS2.
Step 14: RS2 uses the allocated uplink bandwidth to forward the received bandwidth message header to MR_BS.
Step 15: After receiving the bandwidth message header, MR_BS broadcasts the UL_MAP message according to the content of the bandwidth message header. The UL_MAP message contains the information about allocating uplink bandwidth to MS. FIG. 1 shows that MS directly receives the UL_MAP message sent by MR_BS through broadcast. Actually, MS may also receive the UL_MAP message forwarded by relay stations.
Step 16: MS uses the uplink bandwidth allocated by MR_BS to send data packets to RS1.
Step 17: MR_BS broadcasts the UL_MAP message, which contains the information about allocating the uplink bandwidth to RS1. FIG. 1 shows that RS1 directly receives the UL_MAP message sent by MR_BS through broadcast. Actually, RS1 may also receive the UL_MAP message forwarded by RS2.
Step 18: RS1 uses the allocated uplink bandwidth to forward data packets to RS2.
Step 19: MR_BS broadcasts the UL_MAP message, which contains the information about allocating the uplink bandwidth to RS2.
Step 20: RS2 uses the allocated uplink bandwidth to forward data packets to MR_BS.
The inventor found that the conventional technology has at least the following problems:
Each RS, after receiving a bandwidth request from the subordinate network entity, uses its own CDMA ranging code to send a bandwidth request to MR_BS, and after obtaining the allocated bandwidth by parsing the corresponding UL_MAP message broadcasted by MR_BS, RS uses this allocated bandwidth to send the bandwidth request which is received from its subordinate network entity. The latency for the bandwidth request procedure of MS may be increased. Especially when the system has a large number of hops, the RS uses Contention-based CDMA ranging codes to request bandwidth, and in order to contend successfully RS may try several times to obtain bandwidth for forwarding the bandwidth request from MS. Therefore, more delay may be induced in the bandwidth request procedure.